| 摘要 |
1513050 Transistor switching circuits MASCHINENFABRIK RIETER AG 28 Nov 1975 [20 Dec 1974] 48987/75 Heading H3T [Also in Division H2] In a circuit in which an ohmic-inductive load 6, 7 is pulsed by a switching transistor 5, a diode 8 is conventionally provided to allow the load current I 5 to continue to circulate on switch-off, but on switch-on again the diode 8 conducts for a short period until charge carriers are cleared therefrom, temporarily overloading and possibly damaging the transistor: a second diode 9 or non-linear resistive member containing a diode connected in series with the first diode and shunted by a lowohmic inductor 10 prevents rapid growth of the current on switch-on before the first diode blocks. In a circuit in which the load current does not vary much under the rapid on-off cycle of the transistor (Fig. 4, not shown), the v.t. integral of the inductor 10 is chosen large enough to delay rise of current I 6 , but small enough to be lower than the forward drop across the non-linear resistor including diode 9. The choice of inductor is eased by adding to diode 9 other diodes in series (Fig. 5, not shown), a Zener diode (Fig. 6, not shown), or a non-ohmic resistor with V 5 I characteristics similar to the forward characteristic of a diode. The inductor 10 may be allowed to saturate to assist rapid drop of current towards zero before reversal on switch on. The invention may be applied to protection of a transistor chopper providing speed regulation of a D.C. motor (Fig. 10, not shown), and is adaptable to the supply of a relay or power magnet. It is also applicable to protect the transistors of a 3-phase push-pull inverter suppling an inductive lead such as an asychronous motor (Fig. 11, not shown) and to a single inverter stage (Fig. 12, not shown).
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